Systems and methods for monitoring the exhaust gas composition and fine particle composition of exhaust emissions of various types of vehicles are known. For example, with regard to automobiles, it is common for emissions inspection stations (or automotive repair facilities) to utilize dynamometers for controlled engine loading tests for the purposes of exhaust emission measurement. One drawback associated with dynamometer testing, however, is that the measurements acquired often do not represent emissions under actual operating conditions when automobiles are in motion on a roadway or other driving surface.
To remedy these and other drawbacks associated with dynamometer testing, remote emissions sensing systems have been developed to remotely monitor the exhaust gas composition of automobiles traveling past “test sites” located along streets or highways. Examples of remote emissions sensing (or “cross-road”) systems are described in, for example, U.S. Pat. Nos. 5,210,702, 5,319,199, 5,401,967, 5,591,975, 5,726,450, 5,797,682, 5,831,267, and 5,877,862, each of which is hereby incorporated herein by reference in its entirety.
Despite steady advances in the sophistication and robustness of remote emissions sensing systems, the implementation of some such systems may be somewhat time and/or labor intensive. For example, the equipment comprising a remote emissions sensing system is often transported to a test site in a vehicle (e.g., a van), assembled for a testing session, calibrated, disassembled after the testing session, and either transported to a new test site or returned to a central facility where acquired emissions (and other) data may be processed.
Moreover, some remote emissions sensing systems remain susceptible to erroneous readings or inconsistent results. Unfortunately, such drawbacks can sometimes lead to relatively high incidences of discarded data or relatively high incidences of “flagged” test results, which indicate suspect results.
In addition, existing remote emissions sensing systems often utilize external mirrors to direct light beams through vehicle plumes. These exposed mirrors require careful alignment and are subject to alignment drift, degradation from the elements, and/or vandalism. This may present difficulties when deploying such systems without an operator, or when deploying them under adverse weather conditions.
Additionally, existing remote sensing systems can be limited in the number of molecular species that they can monitor with sufficient sensitivity, and in the type of detailed particulate information that they can provide. Current commercial instruments monitor only a few molecular species which typically do not include “air toxics” like formaldehyde, acrolein and 1,3-butadiene. Also, some of these monitors provide only an opacity measurement for particles. An opacity measurement provides little or no information regarding the size distributions or chemical compositions of particulate matter.
These and other problems can reduce the benefits of remote emissions sensing systems.